This invention is generally concerned with monitoring the health of a fluid system and more specifically relates to the detection, and preferably also analysis, of anomalies in a fluid system, for example the detection and analysis of contaminants in a liquid. The invention has particular, although not necessarily exclusive, application in the detection of particulate contaminants in a flowing liquid, for example a flow of oil (e.g. engine lubricating or cooling oil), fuel, coolants (e.g. water) or hydraulic fluid in a power plant or other machinery.
Liquids such as oils, fuels and hydraulic fluids are very frequently used in environments in which they are liable to become contaminated, typically with particulate matter. Taking engine lubricating oils as an example, engine components over which the oil washes are subject to wear, creating small particles, often referred to as xe2x80x9cchipsxe2x80x9d or xe2x80x9cfinesxe2x80x9d, which are entrained in the oil flow.
These particles, and other particulate debris, may indicate engine component wear and are factors in the deterioration of the condition of the oil and may also cause damage to other engine components if allowed to freely circulate with the lubricating oil flow. In-line collectors, such as filters and gauzes, are therefore used to collect the debris, the collectors being checked and emptied on a regular basis.
Collection and analysis of the particulate debris can also provide information about the condition of oil washed components of the engine. For example, an excessive amount of debris can indicate excessive wear of a component and thereby highlight a potential problem. By analysing the debris, in particular its composition, it is also possible to narrow down the number of components from which the debris might originate, making the task of identifying the faulty or problem component an easier one.
However, the regular checking and emptying of the collectors, and the analysis of the collected debris, amount to a burdensome manual maintenance requirement that it would be desirable to avoid. Moreover, the checking and emptying of the collectors are intrusive processes, which must necessarily be undertaken when the engine is not operating.
In addition to the problems associated with contaminants, particulate or otherwise, liquids such as those discussed above, which often work in very harsh environments, tend to experience a gradual deterioration over time. This deterioration may be of the base liquid itself, for example a change in structure or composition, and/or a loss or reduction in the efficacy of intentional additives (liquid or particulate) to the liquid, for example rust inhibitors or friction reducing additives in oil, which breakdown over time. As with the detection of contaminants, the task of monitoring this deterioration, by sampling and analyzing the oil or other liquid, is intrusive and time consuming.
Definitions
It is useful here to set out a number of definitions of terms used extensively in this specification.
The term xe2x80x9cfluid systemxe2x80x9d refers to both liquids and gases, and includes mixtures of more than one liquid, mixtures of more than one gas, and mixtures of liquids and gases.
The term xe2x80x9cadditivexe2x80x9d is used herein to refer to desired or intended additions to the fluid system, added in amounts usually no more than 10% by weight of the fluid system. Additives will usually be liquids or solids (e.g. particulates suspended in the fluid system).
The terms xe2x80x9canomalyxe2x80x9d and xe2x80x9canomaliesxe2x80x9d are intended to refer to unwanted changes in a fluid system, in particular the presence, and more particularly the build up of contaminants, the reduction in the concentration or efficacy of an additive, and/or the deterioration of the fluid or fluids from which the system is composed.
The term xe2x80x9ccontaminantxe2x80x9d refers to foreign, i.e. unwanted, material present in the fluid system, for instance unwanted particulates and liquids, examples of which would respectively be the xe2x80x9cchipsxe2x80x9d referred to above and water in engine oil.
The present invention is generally concerned with monitoring the health of a fluid system, preferably in situ. More specifically, it proposes unique Nuclear Magnetic Resonance (NMR) techniques for the detection, and preferably also analysis, of anomalies in the fluid system. The invention is based on an understanding that the existence of anomalies in a fluid system will often cause detectable changes in the NMR characteristics of the fluid system.
Accordingly, in general terms, there is provided a method for detecting an anomaly in a fluid system, the method comprising exposing a sample of the fluid system to a first, non-oscillating magnetic field, simultaneously exposing the sample to a second, oscillating magnetic field orthogonal to the first field, modulating one or both of the magnetic fields, and detecting and capturing a resulting NMR signal from the sample.
The xe2x80x9cmodulationxe2x80x9d may be a controlled intermittent application of the oscillating magnetic field, i.e. a pulsed NMR approach, various examples of which will be well known to the skilled person. Alternatively, a continuous wave approach may be employed, in which, as will be well known to the skilled person, the modulation may be the variation, typically in a linear fashion, of either the frequency of the oscillating magnetic field or, more typically, the field strength of the non-oscillating magnetic field.
An analysis of the captured signal, typically involving transformation of the signal into an NMR frequency domain spectrum, can be performed to look for specific changes in the signal indicative of the presence of a particular anomaly. The parameters affecting the NMR procedure, including the strength of the non-oscillating field and the frequency of the intermittent, oscillating field if the preferred pulsed NMR approach is employed for example, can be selected in dependence on the anomaly it is desired to detect, as will become more apparent from the following discussions.
More detailed aspects and preferred features of the invention are discussed further below in the context of various embodiments of the invention.